Recurrent bacterial infection is a complaint encountered regularly in the course of both adult and pediatric care. Defects of neutrophils and monocytes are most commonly associated with recurrent infection, but abnormalities of immunoglobulins and complement must be considered. Defensins, small antibacterial peptides, have been implicated recently in some of the infectious diathesis of cystic fibrosis. A thorough history and physical examination focused on severity, sequelae, and microbiology of infections can usually determine whether a patient needs further evaluation. The diseases and syndromes most frequently associated with recurrent infection are presented, along with discriminating clinical, pathologic, and microbiologic features.